Binding bauxite fines into granules with colloidal silica



Patented Jul 15, 1952 por'at'io'n of Delawarev END Drawing. Application-April '26, 1949,

r 2.:, 03,6 9' I I v EBINDINGBAUXI'TE FINEsIN'ro GRANULES W THCQLLOIDA 7 I *1 Heinz fieinemafnm ljrexelf v I "Porocel Corporation, Philadelphim l'a a cor- Serial No. 89,814

The present invention relates to a method or producing bauxite granules from: bauxite fines, which granules have a surface area and'hardness equal or superior to that of bauxitegranules 'pro- 'ducedj;by conventional methods. U f f If:

Bauxite, 'Which is a naturally occurring alumina ore containing some clay, iron, and titania, finds use in a variety of treatments or reactions as an adsorbent, catalyst, and catalyst carrier. In order to produce the granular grades currently marketed, the ore containing 40% to 45% volatile matter (mostly water) is usually dried to about 30% volatile matter, crushed, screened and thermally activated by heating at 600 F. 001200 F. to leave in the granules a volaftile content'between- 1% and 10% by weight. 'In

the course of grinding or milling, some breakdown to fine powder occurs. For example, the smallest mesh size granular bauxite "usually marketed is 40-80, and" any bauxite particles finer than 80 mesh are considered as =fines. This'material is too fine to find use in stationary bed applications such as mineral oil or wax decolorization, or hydrocarbon desulfuriza-tion and'is'omerization, and "many attempts have been "made to form it into granularparticles by chemical or physical means. 7 e have failed either because of the detrimental efiect of the chemicals added on the adsorbent and catalytic properties of the bauxite or' because the resulting-granules were too :soft and disintegrated readily. Granulating"bauxite? fines by 'means of sodium silicate followed by acid'washinghas been suggestedbut' this method is cumv 'bersome, requires considerable equipment and control, and is expensive. Granulating "fines by adding sodium silicate and baking gives aprodnot of poor adsorbent properties due to the presence of sodium ions which are not readily removed: Attempts to granulate fines simplyby moistening with water or organic binders and then's'ubjecting the mixture to'compressio'n, pel- -leti'ng; or extrusion yields a productwhich is only surface hardened and which disintegrates when its outer surface is'cracked orabraded.

I have now found a .method for'produci'ng bauxite granules from bauxite fines which avoids the difliculties of the prior art processes, and which gives hard, resistant granules without loss of surface or porous properties.

- In accordance with my inventiombauxite fines which have been thermally activated at 600 F. 470K200 are impregnated .with 'an aqueous 6 Claims. (Cl;.1252451) Most of these attempts solutionofcolloidal silica having a concentration between 2% and 30% in an amount sufficient-to include material give between 2% and 20%, and preferably and 115%5by weight, of silica inthe bauxite fines.

fines employed in this invention constitute bauxite having a mesh size of or smaller, and which will pass @100. or. a 200,

,gjrjeyenfa 300 mesh screen. These bauxite fines may besa'ked in an excess of the colloidal silica s lution; or. may be mixed wi h, su h an am un of solution as will leave the fines in"'-a moist condition. When an excess of solution is u'sed,

that which .is not soaked up or absorbed'mayjbe drainedoff for reuse. In any event, it is desk.- able to produce a" mi tim oi bauxite .fineSJconta in th r qui ed amount of silica and a volatile matter content (mostly water) ranging "lb?- tween 30% andf40 by wei htiland p erably 3.5% to. 40%;. Avolatilepmatter content between 30%fland 40% is necessary "orderto carrvpil a subsequent process step, i. e. the formingot the fines into pellets or masses. -'The-proper vol a-tile content may-be obtained by adjusting the "quantity and concentration of the colloidal silica solution so that upon mix-ing with the -fines, -the desired volatile 'content {is achieved. Alternatively, the fines may beim'pregnatedwith-a fairly concentrated colloidal silica solution, and then sufficient water is "added to give the desired volatile content. I v 'fThe lfines thus impregnated with colloidal si l ai, Solution are then I-shapedinto si 'b'le masses by compression, tabletting, 'or pelleti g, ,er by extrusion through a die plate fprovidediwith a plurality of small apertures, the pressureen'lploye'd in any of these shaping methods ranging between and 3000 1bs./sq.in. .The bauxite fines may be shaped into granules of final desired .size directly -:by employing tablettin'g, pelleting, or extrusion apparatus havingzdies of there- .quired dimensions, for example, fcylindrical or rounded pellets ,of' f or r finch diameter, oralternatively, the fines containing .the colloidal: silica solution may be formed into larger masses using athe same type of equipment but' :withlarger dies such as to'give pellets of -to 1 inches in diameter. After shaping, the masse may be dried at F. to 220 F. or at temperatures as high as 300. or- 400-F to irreversibly precipitate the silica and thus bond the fines. The dried masses-are then thermally activated by heating at 600 F. to

1200 F., and thereafter, if necessary, reduced to granules of required mesh size by grinding and screening. For example, the granules may-be prod-uced i-n 'm'esh sizes-of 2/4, 4/8, 4/ 10, 4/14, 8/14, 10/30; 20/60; or 40/80. These granules are strong, uniform units which resemble natural bauxite granules produced by conventional methods from raw bauxite ore, and can be used in deep beds without undue break-down and attrition. The physical properties of the granules produced ,from. the fines, such :as, surface area, pore size, ,pore "diameter," adsorbent power, et c., are the same as those of natural bauxite granules, and in many cases the surface area may be I slightly larger.

carriers or supports, are unimpaired oriinproved."

The mixing or impregnation. of the bauxitev fines with the colloidal silica solutiori may be carried out in any suitable apparatus, for example, a plug mill or vessel preferably provided Adsorbent and catalytic properties, as well as the ability to functionfas'eatalyst ,to 2/4 mesh granules. as similar grnesh size granules from natural 4 during plant processing, were wetted with 130 cc. of colloidal silica solution. Such solution was obtained by diluting the above described commercially available colloidal silica solution with water to give 18% by weight S102 concentration. The fines and solution werethoroughly ,mixed, and the mixture iwas compressed in a hydraulic press at 2,000 lbs/sq. in. to give masses -or pellets 1%," in diameter by 1" in length. These pellets were dried at 180 F. to 220 F. and then-calcined at 1100" F. to a volatile matter content of 0.7%, cooled, crushed, and screened These granules, as well bauxite likewise calcined at 1100" F., were subjected to a hardness or break-down test which with a stirring means. After mixing or iin'pr'e'gj nation is accomplished, the moist fines are 'de'- livered to the shaping apparatus such as a con-:

ventional auger extrusion machine provided with an apertured die, plate, and the moist fines ar'e e'xtruded in theform of a plurality of'cylinidricalrods which are cut, or broken intolengths as they issue from the die apertures. For successful extrusion, the volatile matter. content '(water) should be maintained b'etween35% and 'i,40%,1otherwise the extrusion tol'produce fairly "rigid masses is 'difiicult to. accomplish; .In the event that the'massesfor pellets are formedjin "a hydraulic press,"tabletting or pelletin'g masize between 100 and 600 '(angstrom units) r and: should have apI-I between 9.5 and 10.5. Such colloidalsolutionpis neither a true solutionof silica nor a solution-of sodium silicate, and is not tobe confused therewith.

Aicommercially;available colloidal silica solu- F tion which maybe used in,accordance with this .invention has; the following properties:

out in rotary kilns or other Such-colloidal silica solution may be diluted with water without-afiecting its stability. "Cooling the solution-to 32 F. or lower causes the .silica' to be irreversibly precipitated, as does evaporating the water from the solution by heating, preferably at 180 F. or higher. The NazO content serves only to stabilize the colloidal SiO2' and isnot essential" except to maintain stability prior to use. tute sodium silicate, and insofaras this invention is concerned, is withouteifect.

h The-present invention may be further illustrated by the following example, which, how- .ever, is not to bev construed as limiting the scope thereof.

,200 grams of bauxite fines produced as a by- .product in the commercialoperation of a plant formanufacturing; natural bauxite granules, whichfines'had been activated at about 1100 F.

Such NazO does consticomprises tumbling the granules in a. metal cylinder 10 inches in length and 4 inches in diameter rotated at 19 R. P. M. for one hour, and then screening to determine the amount of break-down. The results are presented in the following table and the notations If/4,7178, and T/20. define the percentage .of bauxite passing through a 4mesh' screen, an, 8 mesh screen, and a 20 mesh screen, respectively. ,The smaller thepercentage, the less the breakfdo'wn of the granules.

Break-Down Weight percent Gimmes From this data it-will be seen that the granules produced by binding bauxite fines with colloidal silica were more resistant to breakdown than those obtained in the conventional production of granules from natural ore. .Moreover, the granules produced from fineshave at least equal or greater surface area than natural granules, and are capable of retaining their strength even after impregnation with various catalysts such as metals, their oxides, or their salts. V .Iclaim: V 1. A method for producing bauxite granules from bauxite fines, which comprises mixing with bauxite fines-a colloidal solutionfof silica having an average particle size between 100 and 600 A. and a pH between 9.5 and 10.5 in an amount sufficient to give between 2% and 20% of silica in the bauxite fines, forming the sili'ca-imprege nated fines into masses under a pressure between 100 and 3000 lbs/sq. in., drying the masses, and calcining the dried masses at 600- F. -to 1200 F. v v I 2. A :method for producing bauxite granules from bauxite fines, which comprises. mixingwith bauxite fines a colloidal solution of silicahaving an average particle size between 100 and600 A. and'a pH between 9.5 and 10.5 in an amount sufiicient to give between 2% and 20% of silica in the bauxite fines, forming the silica-impregnated fines into masses under a pressure between 100 and 3000 lbs/sq. in., drying the masses, calcining the dried masses at. 600 F. to -1200 F., and reducing the calcined masses to granules. 3. A method of producing bauxite granules from bauxite fines, which comprises mixing with bauxite fines a colloidal solution of silicahaving drying the extrudate, and calcining the dried material at 600 F. to 1200 F.

4. A method of producing bauxite granules from bauxite fines, which comprises mixing with bauxite fines a colloidal solution of silica having an average particle size between 100 and 600 Av and a pH between 9.5 and 10.5 in an amount sufficient to give between and 15% of silica in the bauxite fines, adjusting the water content of the silica-impregnated fines to a value between 35% and 40% by weight, extruding the mixture at a pressure between 100 and 3000 lbs./sq. in., drying the extrudate, calcining the dried material at 600 F. to 1200 F., and reducing the calcined material to granules.

5. A method for producing bauxite granules from bauxite fines, which comprises mixing with bauxite fines a colloidal solution of silica having an average particle size between 100 and 600 A. and a pH between 9.5 and 10.5 in an amount sufficient to give between 5% and 15% of silica in the bauxite fines and of a concentration such as to give between 35% and 40% by weight of water in the bauxite fines, extruding the mixin., drying the extrudate, and calcining the dried material at 600 F. to 1200 F.

6. A method for producing bauxite granules from bauxite fines, which comprises mixing with bauxite fines a colloidal solution of silica having an average particle size between 100 and 600 A. and a pH between 9.5 and 10.5 in an amount suflicient to give between 5% and of silica in the bauxite, fines and of a concentration such as to give between and by weight of water in the bauxite fines, extruding the mixture at a pressure between and 3000 lbs./sq. in., drying the extrudate, calcining the dried material at 600 F. to 1200 F., and reducing the calcined material to granules.

HEINZ HEINEMANN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. A METHOD FOR PRODUCING BAUXITE GRANULES FROM BAUXITE FINES, WHICH COMPRISES MIXING WITH BAUXITE FINES A COLLOIDAL SOLUTION OF SILICA HAVING AN AVERAGE PARTICLE BETWEEN 100 AND 600 A. AND A PH BETWEEN 9.5 AND 10.5 IN AN AMOUNT SUFFICIENT TO GIVE BETWEEN 2% AND 20% OF SILICA IN THE BAUXITE FINES, FORMING THE SILICA-IMPREGNATED FINES INTO MASSES UNDER A PRESSURE BETWEEN 100 AND 3000 LBS/SQ., IN., DRYING THE MASSES, AND CALCINING THE DRIED MASSES AT 600* F. TO 1200* F. 